linux-kernel - Re: [External] Re: [PATCH 1/2] watchdog: refactor watchdog

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Message-ID: <CAD=FV=XaSP2A7Dufrxt1DUUznF9Yk-qdBY3wbE03x4_L8HJLSQ@mail.gmail.com>
Date: Fri, 5 Sep 2025 16:57:37 -0700
From: Doug Anderson <dianders@...omium.org>
To: yunhui cui <cuiyunhui@...edance.com>
Cc: paul.walmsley@...ive.com, palmer@...belt.com, aou@...s.berkeley.edu, 
	alex@...ti.fr, atish.patra@...ux.dev, anup@...infault.org, will@...nel.org, 
	mark.rutland@....com, linux-riscv@...ts.infradead.org, 
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, 
	linux-perf-users@...r.kernel.org, catalin.marinas@....com, 
	masahiroy@...nel.org, suzuki.poulose@....com, maz@...nel.org, 
	zhanjie9@...ilicon.com, yangyicong@...ilicon.com, mingo@...nel.org, 
	lihuafei1@...wei.com, akpm@...ux-foundation.org, jpoimboe@...nel.org, 
	rppt@...nel.org, kees@...nel.org, thomas.weissschuh@...utronix.de
Subject: Re: [External] Re: [PATCH 1/2] watchdog: refactor watchdog_hld functionality

Hi,

On Wed, Sep 3, 2025 at 4:56 AM yunhui cui <cuiyunhui@...edance.com> wrote:
>
> Hi Doug，
>
> On Wed, Sep 3, 2025 at 1:04 AM Doug Anderson <dianders@...omium.org> wrote:
> >
> > Hi,
> >
> > On Sun, Aug 31, 2025 at 10:57 PM yunhui cui <cuiyunhui@...edance.com> wrote:
> > >
> > > Hi Doug,
> > >
> > > On Sat, Aug 30, 2025 at 5:34 AM Doug Anderson <dianders@...omium.org> wrote:
> > > >
> > > > Hi,
> > > >
> > > > On Wed, Aug 27, 2025 at 3:10 AM Yunhui Cui <cuiyunhui@...edance.com> wrote:
> > > > >
> > > > > Move watchdog_hld.c to kernel/, and rename arm_pmu_irq_is_nmi()
> > > > > to arch_pmu_irq_is_nmi() for cross-arch reusability.
> > > > >
> > > > > Signed-off-by: Yunhui Cui <cuiyunhui@...edance.com>
> > > > > ---
> > > > >  arch/arm64/kernel/Makefile                   | 1 -
> > > > >  drivers/perf/arm_pmu.c                       | 2 +-
> > > > >  include/linux/nmi.h                          | 1 +
> > > > >  include/linux/perf/arm_pmu.h                 | 2 --
> > > > >  kernel/Makefile                              | 2 +-
> > > > >  {arch/arm64/kernel => kernel}/watchdog_hld.c | 8 ++++++--
> > > > >  6 files changed, 9 insertions(+), 7 deletions(-)
> > > > >  rename {arch/arm64/kernel => kernel}/watchdog_hld.c (97%)
> > > >
> > > > I'm not a huge fan of the perf hardlockup detector and IMO we should
> > > > maybe just delete it. Thus spreading it to support a new architecture
> > > > isn't my favorite thing to do. Can't you use the buddy hardlockup
> > > > detector?
> > >
> > > Why is there a plan to remove CONFIG_HARDLOCKUP_DETECTOR_PERF? Could
> > > you explain the specific reasons? Is the community's future plan to
> > > favor CONFIG_HARDLOCKUP_DETECTOR_BUDDY?
> >
> > I don't think there are any concrete plans, but there was some discussion here:
> >
> > https://lore.kernel.org/all/CAD=FV=WWUiCi6bZCs_gseFpDDWNkuJMoL6XCftEo6W7q6jRCkg@mail.gmail.com/
> >
> > -Doug
> >
>
> I’ve read your linked content, which details the pros and cons of perf
> watchdog and buddy watchdog.
> I think everyone will agree on choosing one as the default.
> It seems there’s no kernel/watchdog entry in MAINTAINERS—what’s next
> for these two approaches?

I guess to start, someone (you?) should send some patches to the list.
Maybe one patch to make buddy the default and one to change the
description of the "perf" lockup detector say that its usage is
discouraged, that it might be removed, that people should use the
"buddy" detector instead, and that if there's a reason someone needs
the "perf" detector instead of the buddy one then they should make
some loud noises.

You'd want to CC folks who were involved in recent watchdog changes
and make sure to CC Andrew (akpm). If folks react positive and Andrew
agrees then he'll likely land the the patches and we'll have made
forward progress. :-)

-Doug